Is there an actual reason for it, apart from Apple hurrying devs along?

For the consumer, the benefits of backwards compatibility are obvious, but it’s sad that companies don’t see it as a selling point.

Well, we wouldn’t want anyone using their perfectly functional copy of Photoshop CS6 would we…

The Apple Silicon dev kit shipped in 2019 and the cutoff date is 2028, so it's a pretty mild form of hurry.

If you want to continue to run older software, do what Windows 11's compatibility layer does and spin up VM with an older version of the OS.